1. Field of the Invention
This invention relates to an oxide type solid lubricant which maintains outstanding lubricity in the open air or in an oxidizing atmosphere over a wide temperature range of from room temperature to about 1,000.degree. C.
2. Description of the Prior Art
The mechanical elements of various high temperature devices such as, for example, the flow path control devices in supersonic jet engine combustion chambers, the mechanical seals in the combustion chambers of ceramic gas turbines, and the drive components in MOCVD devices are frequently exposed to changes in temperature within the range of from room temperature to elevated temperatures. However, oil lubrication cannot be used at elevated temperatures and it is difficult to obtain solid lubricants that are able to maintain their lubricity up to a temperature of around 1,000.degree. C. The mechanical elements must therefore be cooled by a suitable means or be isolated from regions heated to elevated temperatures, which entail complication of design. If a lubricant can be developed that functions stably within such wide temperature range, the devices could be simplified without a need to resort to a complex or unreasonable design, since materials that are resistant to high temperatures have been developed for use in the construction of such devices.
Solid lubricants in common use include non-oxide type solid lubricants such as graphite and MoS.sub.2, which under atmospheric conditions can be utilized in temperature ranges having an upper limit of about 500.degree. C. In contrast, oxide type solid lubricants are stable and can resist oxidation at elevated temperatures, and either exhibit high coefficients of friction at room temperature and an upper working temperature limit of around 600.degree. C. to 800.degree. C., or melt and exhibit lubricity only at elevated temperatures. Thus, there is as yet no solid lubricant that is stable and exhibits lubricity over a wide temperature range of from room temperature to about 1,000.degree. C. while also satisfying the various other requirements.
In response, U.S. Pat. No. 5,100,848 proposed a solid lubricant formed of a sintered composite ceramic material resulting from mixing and sintering powders of Na.sub.2 ZrO.sub.3 and Cr.sub.2 O.sub.3. In this process part of the chromium is replaced by zirconium to form a solid lubricant having good cleavability, and it is effective in that the solid lubricant exhibits outstanding lubricity at temperatures ranging from room temperature to about 1,000.degree. C.. However, it was found that this solid lubricant has various problems, such as that when left in the open air it absorbs moisture and exhibits deliquescence, it starts to melt at 730.degree. C., and its lubricating properties are affected by slight differences in forming conditions.
An object of this invention is to provide an oxide type solid lubricant which does not exhibit deliquescence when left in the open air or changes in lubricating properties caused by slight variations in forming conditions, and stably exhibits outstanding lubricity in the open air or in an oxidizing atmosphere over a wide temperature range of from room temperature to about 1,000.degree. C..